Medical catheters are widely used to provide access to locations within a body to treat diseases. Medical therapy devices may be connected to an end of the catheter and the catheter steered within the body to position the therapy device at the treatment location. For example, cardiac arrhythmias may be treated by the ablation of specific heart tissue found to be causing arrhythmia. Ablation may be performed by a number of techniques, including the local application of energy, for example, radio frequency energy, or by the application of cryogenic temperatures to the site of the problem tissue. An ablation electrode may be a therapy device at or near the end of the catheter for providing the radio frequency energy. An ablation balloon may be a therapy device at or near the end of the catheter to for providing the cryogenic temperatures.
The specific heart tissue responsible for arrhythmia in a patient may be identified by moving a mapping catheter having one or more electrodes around the interior of the heart and measuring cardiac signals to sense changes in the electrical fields. A map of the electrical conductivity of the heart may be formed from the measurements to identify abnormalities which may be candidates for ablation. Some mapping catheters are designed such that the electrodes may physically contact the heart wall, including flexible designs that are inserted in a compact form and later deployed into a basket-like array. Such an electrode array may be a therapy device at or near the end of the catheter for mapping the electrical conductivity of the heart.
Particularly useful steerable catheters are those in which the end with the therapy device may be deflected in two different directions. Such catheters require a steering control apparatus able to reliably deflect the end of the catheter in both directions.